Spain is famous for its weather, Benidorm, Spanish food, it's football team, Barcelona, and basically being a rather sunny place overall â none of these descriptions are incorrect, and in fact they are all entirely true!
As the temperature of the air increases its density decreases. Therefore the thrust produced by the engine decreases. As the air pressure increases, its density increases, causing thrust produced by the engine to increase. Altitude has a double effect on thrust. As the altitude increases, the air becomes colder and denser, up to the beginning of stratosphere. This causes the thrust to increase.
When ambient air pressure is higher (for a given temperature), the density of the air will be higher, so buoyancy will be increased - just slightly. There is pressure above you pushing down and trying to increase your weight, but there is just as much pressure below you pushing up trying to decrease your weight. So they ALMOST balance out. But, there's actually slightly more air pressure below you than above you, so the overall total effect is that your weight actually gets decreased. This is the upward thrust you speak of, otherwise known as buoyancy. It takes the pressure above you into account. Thanks , for appropriate explanation.